Preparation of straw cellulose



Patented Dec. 8, 1953 UN I TED STATES UF FI (IE 2,662,012 PREPARATION OF sTRAW emomse fieee niieiik leu' iiissen, Netherlands,

in] No. 151,299

"Glaifiis prioiity, application Netherlands July 29, 1949 '2 name.

fi he present inventionrelates to the treatment of straw and more particularly to a process for the 11reparation ;oi straw cellulose suitable for -manufacturinghigh gr ade paper. n When preparing cellulose-from w0od according to the -sulphate process, lthe wood is digested in an aquleou s alkaline solution containing 20 sodium hydroxide and sodiumsulphide based on the 'weight of thedry wood the quantity of water usedjoeing dependent on the type of apparatus and process einployed generally this quantity of water varies between two and seven times t ee-we t f th 'w 'sl- J E e i 2 lulose isin the neighborhood of 50% of the dry wood; o e er, sarn'e process applied to straw w s bo t 50% 1 th r sa e the paper manufactured frorn this cellulose is of poor quality-in that it liasa l0w tensile strength andalow number of double folds. -'l-he double t ds ond t d-in a W l es. thaw eds the paper firstf-in one 'directionand then in the opposite direction and the emp ror bends be f ore ;;the ;paper breaks determines "the number of double folds.)

It'is also well known "to treat *straw with acid to effect prehydroly-sis before digesting in an alkalinesolution. By'suchatreatment a cellulose with high alpha-cellulose content isthe'n fibtain'd, which is 'a suitableraw material f01 theniieinufature pf rayon, but in using this method for straw;the-cellulose yield is ueereased vhiihthi, i; 'e-.,-to'about 7 and thec'ellu- 16st bbtaiiled is not earn-tummy suitable for injanufacturing'paper. 7

It is possible 'to prepare "a straw cellulose in practical 6101s and "suitable for manufacturing per tilizing'a 'two sta digestion treatp Ynnt; 'Th'e first step-consists ofpartiallwdigesting the straw in 'a weak alkaline solution and completing the treatment neans of gaseous mmfinermmn Patent No 63,978).

the chemicals is considerably less than hitherto required.

It is afurther objectof this-invention to produce a high grade,cellulosesuitable for manufacturing [paper which in turn has improved physical and chemical properties. H

Other objects andadvantages of the invention will be apparent from -the following detailed-description. w

According tothisinvention, straw is introduced into an aqueous alkaline-solutionanddsdiested therein for --from;-2 to 3 hours, :preferably ior about 2 hoursand 15 minutes. *Ihe-temperature of the solution is maintamed between ll5 -C.--and 130 (3., preferably atabout 120? G. The total alkaline agents employed are not less than 7% and-not more than 9% "basedon the 'weight'of the dry straw and consist of about 80% sodium hydroxide and about 20% sodium sulphide. These percentage ranges can be satisfied if the sodium hydroxide: varies from 5.6% to 7.2% While thesodium sulphide varies from 124% to 1.8%.

An'ra t e opti rmrementaa 9 t kaline agents based on the Weight of the art straw are 6.4% sodium hydroxide and 116% so'dium sulphide.

It was determiiiejd that the best results were achieved when the digesting operation took place using a straw liquid ratio of 1:2. The strawliquid ratio is thefifatio foifthe weightritthe 'stra'w (in-kg.) to "the Volume of the liquid (in liters). Since the 'di ils'traw retains certain amount of moistufe 'froin the atmosphere, fthe infoisture jcontentof emery straw inust be taken into "consideration. Thus, 'if the air-dry "straw contains 10% of moistureand 100 kg. are used, inorder to provide an aqueous alkaline solution of 631% sodiumhydroxideahd 16% sodium sul phid'egit isnec'elssary to use 0.064 or 5.76 kg sodium hydrogiide and 90x 0.016 or 1.44 kg. sodium sulphide. i'Th'ese alkaline agents "are dissolved 'in a totalliquidvolume of (2X90)10 or 179 i livel r; H i W In reaching the conclusions that aboutl'fiilfC'.

is the most desirable temperature-for the-digest: 'ing operation, and that about"6.'4%--sodium 'h'y 'droxide and about '1.6% *sodiunrsulphidebased on the weight of the dry stra are-tHe most satisfactory etiree-nuances'er alkali an the 'solutioii; everal experiments were condueteu warying these' conditions hispartimilartempera ture and these partied r 'cncentrations, itwas determined that the highest yield of cellulose was obtained while the subsequent removal of the lignin was effected with the least amount of chlorine. Moreover, the properties of the paper manufactured from the straw cellulose were excellent.

In the first series of experiments, the straw was digested in an aqueous alkaline solution maintained at different temperatures. The straw-liquid ratio was 1:2, and the alkaline solution contained 6.4% sodium hydroxide and 1.6% sodium sulphide, based on the weight of the dry straw. In each experiment the air-dry straw contained moisture and the digesting operation was conducted for two and one-quarter hours. Table I given below confirms the fact that the highest yield of cellulose and the lowest consumption of chlorine was obtained at 120 C..

The following table involving the same series of experiments shows that the properties of the paper manufactured from the straw cellulose were extremely better when the digesting opera tion took place at 120 C. as compared with the operation in which the digesting took place at 160 C. The breaking length in km. refers to the length of paper that breaks under its own weight when freely suspended from a support.

Table II Breaking Number Temperature lengthin of double km folds Additional experiments showed that when digesting at 120 C., decreasing the alkali content did not give an improvement in the cellulose yield and had the disadvantage that the chlorine consumption was greater. The results of these experiments are tabulated as follows:

Table III Chlorine e e ater Percent tion 1n ercent Temperature NaOH-lpercent czficulated Nags calcuated on dry 011 ry cellulose Straw Increasing the sodium hydroxide and sodium sulphide content gave no better results insofar as the cellulose yield was concerned, even when the temperature was decreased. This is clearly shown from the following table.

Table IV Cellulose gel-001%}; yield 11% a percen Temperature percent calculated Nil-2S on dry straw It can be seen from the above tables that the best all around results are achieved when using the amounts of alkali and temperature mentioned in the first series of experiments. Therefore, the processes of the invention are considerably cheaper with respect to the chemicals used, including the chlorine consumption, which materially reduces the expense of the operation, and in addition the process gives a higher yield of cellulose which is particularly well suited for the manufacture of high grade paper.

What is claimed is:

1. A process for the preparation of straw cellulose suitable for manufacturing paper which comprises digesting the straw for a period of time not more than about 3 hours and not less than about 2 hours in an aqueous solution consisting essentially of sodium hydroxide and sodium sulphide maintained in a temperature range between C. and 130 C. and having a total content of alkaline agents from 7% to 9% based on the weight of the dry straw, said alkaline agents consisting of about 80% sodium hydroxide and about 20% sodium sulphide, the

straw-liquid ratio being about 1:2.

2. A process for the preparation of straw cellu lose suitable for manufacturing paper which comprises digesting the straw for a period of time not more than about 3 hours and not less than about 2 hours in an aqueous alkaline solution maintained at a temperature of about C. and consisting of about 6.4% sodium hydroxide and about 1.6% sodium sulphide, each based on the weight of the dry straw, the straw-liquid ratio being about 1:2.

PIETER HENDRIK TEUNISSEN.

References Cited in the file of this patent UNITED STATES PATENTS Number Name Date 296,935 Dahl Apr. 15, 1884 1,626,171 Wells Apr. 26, 1927 1,634,603 W'ood July 5, 1927 1,692,774 Graiiiin Nov. 20, 1928 1,816,456 Zimmerman July 28, 1931 1,920,239 Bori et al Aug. 1, 1933 2,049,567 Larson et a1 Aug. 4, 1936 2,099,400 Jones Nov. 16, 1937 2,161,763 Jones June 6, 1939 2,482,142 Chidester et a1. Sept. 20, 1949 FOREIGN PATENTS Number Country Date 40,620 Austria Jan. 25, 1910 27,940 Norway May 12, 1917 313,344 Germany July 7, 1919 356,120 Italy Jan. 25, 1938 OTHER REFERENCES Singh: Chemical Abstracts, vol. 37, pp. 4568, 6454.

Wells et al.: Paper Trade J., August 28, 1941, pp. 39-42.

Hanson: Paper Trade J.,- January 9, 1941, pp. 32-38. 

1. A PROCESS FOR THE PREPARATION OF STRAW CELLULOSE SUITABLE FOR MANUFACTURING PAPER WHICH COMPRISES DIGESTING THE STRAW FOR A PERIOD OF TIME NOT MORE THAN ABOUT 3 HOURS AND NOT LESS THAN ABOUT 2 HOURS IN AN AQUEOUS SOLUTION CONSISTING ESSENTIALLY OF SODIUM HYDROXIDE AND SODIUM SULPHIDE MAINTAINED IN A TEMPERATURE RANGE BETWEEN 115* C. AND 130* C. AND HAVING A TOTAL CONTENT OF ALKALINE AGENTS FROM 7% TO 9% BASED ON THE WEIGHT OF THE DRY STRAW, SAID ALKALINE AGENTS CONSISTING OF ABOUT 80% SODIUM HYDROXIDE AND ABOUT 20% SODIUM SULPHIDE, THE STRAW-LIQUID RATIO BEING ABOUT 1:2. 